1. Regulation of the Cell Cycle

2. Internal and External Factors
There are many potential reasons why a cell would not be ready to divide
Kinetochores not attached to microtubules
Density dependent inhibition
Anchorage dependence, where cells have to be attached to a substratum (solid surface) to divide

3. Cells anchor to dish surface and divide (anchorage dependence).
When cells have formed a complete
single layer, they stop dividing
(density-dependent inhibition).
If some cells are scraped away, the
remaining cells divide to fill the gap and
then stop (density-dependent inhibition).
25 µm
Normal mammalian cells

4. Molecular Control
Since the cell cycle is known to be controlled both internally and externally, now we must ask what controls it
Sequential?
Experiments have shown that proteins are responsible

5. Experiment 1 Experiment 2 S G1 M G1 S S M M When a cell in the M phase
The Rao Johnson Experiment
Experiment 1
Experiment 2 S G1 M G1 S S M M
When a cell in the M phase
was fused with a cell in G1,
the G1 cell immediately began
mitosis—a spindle formed and chromatin condensed, even though the chromosome had not been duplicated. Something in M phase induced interphase cells to divide.
When a cell in the S phase was fused with a cell in G1, the G1 cell immediately entered the S phase—DNA was synthesized. S cells contained something that induced regulation in G1 cells.

6. Conclusion: the S phase proteins work on G1 nuclei, M phase works on everything
Biologists named these proteins “cyclins”
These are used in all three portions of interphase
Each is referred to as a “checkpoint”
Collectively, they are called growth factors
The cell has mechanisms that ensure each phase is complete before moving onto the next
We have seen this already with the possibility of a cell entering G0

7. LE 12-15 G0
G1 checkpoint G1 G1
If a cell receives a go-ahead signal at the G1 checkpoint, the cell continues on in the cell cycle.
If a cell does not receive a go-ahead signal at the G1 checkpoint, the cell exits the cell cycle and goes into G0, a nondividing state.

8. Cancer Cancer can be thought of as uncontrolled growth of cells
They can lack the mechanisms, do not respond properly to them, or have an error in the pathways
If they stop, it is at a random point

9. Cancer cells do not exhibit anchorage dependence
or density-dependent inhibition.
25 µm
Cancer cells

10. A mass of cancer cells is known as a tumor
If this tumor stays in the original site – benign
If it spreads to surrounding tissue - malignant
A individual tumor cell can break free from the group and invade other organs
It is said to have metastasized
Metastasis
Unfortunately, these cells can continue to grow if supplied with nutrients
Normal cells divide before dying

11. Cancer Lymph vessel Tumor Blood vessel Glandular tissue Metastatic
Cancer cell
A tumor grows from a
single cancer cell.
Cancer cells invade
neighboring tissue.
Cancer cells spread
through lymph and
blood vessels to
other parts of the
body.
A small percentage
of cancer cells may
survive and establish
a new tumor in another
part of the body.

12. Treatments
The two most common treatments we have are chemotherapy and radiation treatments
Chemotherapy
By definition, treatment of any condition via chemicals
Our focus is on antineoplastic drugs – cancer fighters
Act by targeting rapidly dividing cells
However, this also includes healthy cells such as bone marrow (blood cells), hair follicles, and sex cells

13. Common side effects – hair loss and an compromised immune system
Essentially theory is the drugs will kill the cancer faster than the patient
If not discovered soon enough, treatment would take too long
Radiation Therapy
Beam of subatomic particles that damages DNA
Has to focus on a tumor

14. Alternatives
With more knowledge on mechanisms of cancer, new treatments are being proposed
Viruses are being designed to specifically target cancer cells